Best Cat's to put in a offroad y pipe
 

Need some cat's for more low end torque i don't have enough backpressure any suggestions

Magnaflow tiny cats here, installed at Mufflex. No dyno numbers, but on the road course they seem to be a good balance of flow and backpressure. Pulls nicely against heavier LS3 Vettes out of the corners as well as on the long straights.

if you're running any type of cat back you dont need cats for back pressure, it wont make any difference